Railway traffic controlling apparatus



A Ang. 1s, 1.942. w, PLACE 2,293,307

RAILWAY TRAFFIC CONTRLLING APPARATUS Filed Dec. 31, 1940 Ill/6' N500 lTame Tnze Curran# ng.

Tim@ [1745' ATTORN EY Patented Aug. 18, 1942 RAILWAY TRAFFIC CONTROLLINGAPPARATUS Willard P.`Place, Wilkinsburg, Pa., assignor to The UnionSwitch & Signal Company, Swissvale, Pa., a corporation of PennsylvaniaApplication December 31, 1940, Serial No. 372,432

(Cl. 246-63) y 7 Claims.

My invention relates to railway traiiic contr-olling apparatus, and moreparticularly to train carried train control apparatus responsive tocoded energy.

Train carried train control apparatus responsive to coded energy is wellknown. 'Ihe `coded current is supplied across the track rails of a tracksection at the exit end of the section so that when a train occupies thesection current flows along one rail through the wheels and axles of thetrain (train shunt) and back the other rail and consequently suchcurrent iiows in opposite directions in the rails at any given instant.Two inductors are mounted on the train ahead of the leading pair ofwheels with one inductor over each rail and there is an electronictiveforce induced in each inductor in response to each on `period of thecoded current. The two inductors have heretofore been connected togetherso that the electromotive forces induced therein due to current flowingin opposite directions 'in the two rails at any given instant add theireffects and the resultant electr-emotive force is applied to the inputterminals of a train carried amplifier to operate a code following relayconnected to the output side of the arnplifier. The practice has been touse alternating current of the order of 100 cycles per second and tocode such current by periodically interrupting the current at the ratesof 180, 120 and 75 times per minute according to clear, approach-mediumand approach traic conditions in advance of the track section. In somesystems only two code rates of 180 and 75 interruptions per minute areused to reflect clear and approach traffic conditions, respectively.

The length of the track section is predetermined in part according tothe desired spacing of trains and according to the braking distancerequired for the trains operating over the section. The braking distancerequired depends upon the maximum permissible speed and the nature ofthe equipment, such as passenger or freight cars. The high speedsprescribed for present day traliic in both freight and passenger trainservice, require relatively long braking distances and hence arelatively long track section ii a train is to be brought from maxim-umspeed to a sto-p in a single track section. It has been proposed toprovide track sections of the order of 11,000 feet in length where hightrain speed prevails. Broken rail protection is also essential in suchrailway signaling systems. A single track circuit for a track section of11,000 feet may not provide satisfactory broken rail protection whenalternating current of cycles per second is used. Consequently such11,000 foot track section may require that it be provided with one ormore cut section locations to divide the section into subsections eachof which includes a track circuit. Such cut section locations add to theapparatus required and correspondingly increase the cost.

It has ,been proposed to use alternating current of a low frequency andcurrent of 20 cycles per second has been considered. Furthermore, codeddirect current has been proposed. When alternating current of thefrequency of the order of 20 cycles per second or when coded directcurrent is used then satisfactory lbroken rail protection may beobtained for track circuits of 11,000 feet in length. Operatingdifliculties have been experienced when coded low frequency alternatingcurrent or -co-ded direct current is used, because of the possible falseVenergization of the train carried amplifier produced by the so-calledmagnetized spots in the track rails. Such magnetized spots occur atrandom fand act to induce an electromotive force in the train carriedinductors as the train 'moves over the rails. Such inducedelectronic-tive force when amplified may adversely affect the operationof the code following relay.

In View of the above cited conditions `a feature of my invention is theprovision of railway trafc controlling apparatus incorporating novel andimproved train carried train control apparatus responsive to codedenergy.

Another feature of my invention is the provision of a novel and improvedelectron tube amplier for train carried train control apparatus.

An additional feature of my invention is the provision of train carriedtrain control apparatus which is effectively operated only when twoinductors, one over each rail, arel excited by magnetic fieldssubstantially in phase with each other, and random magnetic fields,which excite one inductor only or which excite both inductors but atdiiierent times or which excite both inductors at the same time but donot induce voltages which are in phase with each other, do not cause aneective operation of the` apparatus.

Still another feature of my invention is the provision of novel traincarried train control apparatus 4having two receiving lchannels throughwhich energy is received for controlling the operation of a codefollowing relay and wherewith the energy received by one channel mustbear a predetermined relationship with the energy received by the otherchannel in order to cause an operatic-n of the relay.

Again, a feature of my invention is the provision of railway traiiccontrolling apparatus incorporating an electron tube ampliiier wherewithoperation cf a code following relay coupled to the plate circuit o-f theelectron tube is operated only when two control electromotive forces inphase with each other are simultaneously applied one to each of twodifferent control grids of the tube.

The above features of my invention, as well as other advantages whichwill be apparent as the specification progresses are attained accordingto my invention by providing two inductors mounted on the train inadvance of the leading pair of wheels with one inductor over each railand by applying the electromotive forces induced in the inductors to twodifferent receiving channels. An electron tube having two grids isprovided and one grid is excited by the electromotive force applied toone receiving channel and the other grid is excited by the electromotiveforce applied to the other channel. A code following relay is coupled tothe plate circuit of the tube and the tube is biased so that normally noplate current flows and the bias is high enough so that no current flowsif only one grid is excited by the electromotive force applied to therespective receiving channel. Plate current ows only when the twoelectromotive forces are applied to the two grids of the tubesimultaneously and in phase or at least plate current suicient tooperate the code following relay flows only when both grids are thusexcited.

I shall describe one form of apparatus embodying my invention, and shallthen point out the novel features thereof in claims.

In the accompanying drawings Fig. 1 is a diagrammatic view showing oneform of apparatus embodying my invention when used with train carriedtrain control apparatus. Figs. 2, 3, 4 and 5 are diagrams illustratingoperating characteristics of the apparatus of Fig. 1.

Referring to Fig. 1, the reference characters la and lb designate thetrack rails of a stretch of railway over which traiilc normally moves inthe direction indicated by an arrow and which rails are formed by theusual insulated rail joints into a track section D-E, which may be onesection of a series of consecutive sections of a signal system. Thetrack section D-E is provided with a track circuit comprising a sourceof coded current connected across the rails at the exit end of thesection and a code following relay connected across the rails at theentrance end of the section. The immediate source of current for thetrack circuit of section D-E is a track transformer TD whose secondarywinding 2 is connected across the rails at the exit end D over wires 3and 4, a current limiting impedance 5 being interposed in wire 4. Aprimary winding 6 of transformer TD is connected to a suitable source ofalternating current, such as a generator, not shown, but whose terminalsare indicated at BX and CX, over contacts of a code transmitter CT and acontact of a control relay HD. The source of alternating current may beof any convenient frequency and may be for example of the order ofcycles per second.

The code transmitter CT may be of any one of several forms and is shownas of the relay type whose operating winding is permanently connected tothe terminals BX and CX of the current source, and energized to causeoperation of two code contact members 'l5 and H10, the arrangement beingsuch that contact member 15 is operated to engage a contact 15a at therate of 75 times per minute, and contact member |80 is operated toengage a contact |8316!r at the rate of 180 times per minute. The relayHD is oontrolled by traffic conditions in advance of the section D-E andsuch control apparatus is not shown since it would be in accordance withstandard practice and forms no part of my present invention. It issuiiicient to point out that relay HD is picked up when the section nextin advance of section D-E is unoccupied and is released when suchsection in advance is occupied. When relay HD is picked up closing frontcontact l, a circuit easily traced is completed by which current issupplied to primary winding 6 of transformer TD over code contact l-laof code transmitter CT, and when relay HD is released closing backcontact 8, the primary winding 6 of transformer TD is connected to thecurrent source over code contact 'l5-15a of the code transmitter. Itfollows that when the section next in advance of section D-E isunoccupied and relay HD is picked up, alternating current coded at thecode rate of 180 interruptions per minute is supplied to the track railsof section D-E, and when the section next in advance is occupied andrelay HD is released, alternating current coded at the code rate of 75interruptions per minute is supplied to the track rails of section D-E.

A code following relay ETR is connected across the rails at the entranceend E of section D-E through a transformer rectier shown conventionallyat ER and hence when the section D-E is unoccupied, that is, when thetrain shown conventionally at TV does not occupy the section, trackrelay ETR is operated at the code rate of the current supplied to therails through track transformer TD inthe manner explained above. Thetrack relay ETR would be used to govern apparatus including a controlrelay for the section next in the rear of section D--E and which relaywould be similar to relay HD governed by traic in the section next inadvance of section D-E. This apparatus governed by relay ETR is notshown for the sake of simplicity, since as stated hereinbefore suchapparatus forms no part of my present invention and would be inaccordance with standard practice.

It is to be understood of course that my invention is not limited to thecode rates of 180 and 75 interruptions per minute of the track circuitcurrent, but such code rates are used for illustration since they are ingeneral use. Also that while a low frequency alternating current of theorder of 20 cycles per second may be preferred the alternating currentmay be of a higher frequency such as, for example, cycles per second asis commonly used in railway signaling systems of the type herecontemplated, or the alternating current may be of a frequency evenlower than 20 cycles per second, or the current may be coded directcurrent.

The train shown conventionally at TV is provided with train carriedtrain control apparatus embodying my invention and which apparatuscomprises inductors 9 and Il), two receiving channels to be shortlydescribed, a first and a second amplifier tube VTI and VTS, a codefollowing relay MR, a decoding unit DU and a cab signal CS together withsuitable sources of current.

The inductors 9 and I@ are preferably alike and are mounted on the trainahead of the leading pair of Wheels and in inductive relation to railsIa and Ib, respectively. It follows that when train TV occupies sectionD-E and there is no other train between it and the exit end D of thesection, an electromotive force is induced in each inductor 9 and I0during each on period of the coded track circuit current and suchelectromotive forces have the same frequency and code rate as the railcurrent. Since at any given instant the current flows along rail Iathrough the train shunt and back rail Ib the current in each of the tworails is of substantially the same magnitude so that the electromotiveforces induced in inductors 9 and I0 are of substantially the samemagnitude and are in phase with each other. 'I'he inductors 9 and I0 areconnected to a rst and a second receiving channel, respectively. Thefirst receiving channel comprises a transformer TI and a first gridcircuit for electron tube VTI, While the second receiving channelcomprises a transformer T2, another electron tube VT2, anothertransformer T3 and a second grid circuit for the tube VTI To beexplicit, inductor 9 is connected to a primary Winding II of transformerTI of the first receiving channel through a condenser I2. A condenser I3is connected across a secondary Winding I4 of transformer TI andsecondary winding I4 and condenser I3 in multiple are interposed in arst grid circuit for electron tube VTI, which circuit can be traced fromcontrol grid I5 of the tube over secondary winding I4 and condenser I3in multiple, a biasing battery I6 and to a cathode II of tube VTI.Transformer TI together with condensers I2 and I3, are tuned toresonance at the frequency of the track circuit current and in thisinstance are tuned to resonance at the frequency of cycles per second.It is clear that when an electromotive force is picked up by inductor 9a corresponding electromotive force is made to appear across secondarywinding I4 of transformer TI and this latter electromotive vforce isapplied across grid I5 and cathode Il of the electron tube VTI,

Tube VTI may take different forms, and in Fig. 1 is shown as an indirectheater type tube having ak plate I8, a first or control grid I5, acathode I'I, a second or screen grid I9 and a lament 20.

Inductor I0 is connected to primary Winding condenser 23 in multiple areinterposed in a grid circuit of tube VT2 which grid circuit can betraced from a control grid 25 of tube VT2, over Ysecondary Winding 24and condenser 23 in multiple, a biasing unit 29 and to a cathode 2l oftube VT2. Transformer T2 and condensers 22 and 23 are tuned to resonanceat the frequency 0f the coded track circuit current and hence wheninductor I0 picks up an electromotive force a correspondingelectromotive force is made to appear across winding 24 of transformerT2 and this latter electromotive force is applied across grid 25 andcathode 2I of tube VT2. Electron tube VT2 is an indirect heater typetube having a plate 28, grid 25, cathode 2l and a filament 29.

The train TV is provided with a suitable source of current which may bethe usual 32 volt generator or'battery, not shown, but whose positiveand negative terminals are indicated at B32 and N32, respectively. The32 direct volts of the train carried source is converted into aconvenient higher voltage as required for the plate circuit of the tubesthrough a motor generator MG, the motor element 3| of Which is connectedacross terminals B32 and N32 of the train carried source and thepositive and negative terminals of the generator element 32 of which aredesignated B300 and N300 as Will be apparent by an inspection of Fig. 1.The laments 20 and 29 of tubes VTI andVTZ are connected across terminalsB32 and N32 over parallel circuits easily traced, current limitingresistors 30 and 1I being preferably interposed in the circuits offilaments 20 and 29, respectively.

`A plate ycircuit for tube VT2 is formed from terminal B300 over Wire33, primary Winding 34 of transformer T3, plate 28 and intervening tubespace to cathode 2'1 of tube VT2, biasing unit 26 and wire 35 to thenegative terminal N300. A secondary Winding 36 of transformer T3 isconnected across grid I9 and cathode II of tube VTI over Wires 3l and 38to complete the second receiving channel. It is to be seen thereforethat the electromotive force picked up by inductor I0 is applied to tubeVT2 and is amplified in the plate circuit of that tube and acorresponding electromotive force is then applied from the secondaryWinding 30 of transformer T3 to the screen grid I9 and cathode II oftube VTI. The electron tube VTI is provided With a plate circuit Whichextends from terminal B300 over wires 33 and 39, a primary Winding of a.coupling transformer T4, plate I8 and intervening tube space to cathodeII of tube VTI, and Wires 30, 4I and 35 to negative terminal N300.

The battery I0 which is interposed in the iirst grid circuit of tu-beVTI provides a negative grid bias Voltage for that tube of such a degreethat normally no current Hows in the plate circuit of tube VTI.Furthermore, the bias effected` by battery I5 for tube VTI is highenough that no plate current flows even if the grid I9 is excited by theelectromotive force induced in inductor I0 and applied to the tubethrough the second receiving channel unless the control grid I5 is alsoexcited and driven in the positive direction to some extent. Again, ifcontrol grid I5 is excited by the electromotive force induced ininductor l9 and applied to the first receiving channel and grid I9 isnot excited at the same time no effective plate current flows. Whengrids I5 and I9 are excited and both driven in the positive direction bythe electromotive force applied through the respective receiving channelthen plate current flows and energy is transferred to the secondaryWinding 42 of coupling transformer T4. A Icondenser 43 is connectedacross secondary winding 42 of transformer T4 and the two in multipleare interposed in the grid circuit for the second amplifying tube VT3,the circuit including a grid 44 of tube VT2, secondary Winding 42 andcondenser 43 in multiple, a resistor 45 and a cathode 46 of the tube.

Electron tube VT3 is of the indirect heater type having a plate 4'I,grid 44, cathode 4B and a filament 48, the latter of which is heatedover a simple circuit connected to the B32-N32 current source. The platecircuit for tube VT3 includes terminal B300, a primary winding 49 of anoutput transformer T5, plate 4l and intervening tube space to cathode 46of tube VT3, resistor 45, wires 4I and 35, and terminal N390. Tube VT3is -biased to have a given normal value of plate circuit current andhence energy transferred through transformer T4 to the grid circuit oftube VT3 is amplihed and reproduced in the plate .circuit of the tubeand such variations in the plate circuit current in turn causeanelectromotive force to be induced in a secondary winding Eil of theoutput transformer T5.

Code following relay MR is a polar relay of the type whose contactmember 5I remains in the position to which it was last moved when therelay is deenergize Relay MR is connected to Secondary Winding 5G oftransformer T5 and the arrangement is such that the electromotive forceinduced in secondary winding 50 due to an increase in the average valueof the plate circuit current for tube VTS energizes relay MR at apolarity such that contact member 5l is operated to the left-handposition as viewed in Fig. 1 to engage a normal contact 52, and theelectromotive force induced in secondary winding 5i! due to a decreasein the average value of the plate circuit current of tube VTS energizesrelay MR as required to operate its contact member 5i to the right-handposition to engage reverse contact 53. When relay MR is operated tocause its contact member 5I to alternately engage contacts 52 and 53,direct current is alternately supplied to two portions of a primarywinding 5ft of a decoding transformer AT and an alternatingelectromotive force is induced in secondary winding 55 of transformer AThaving a frequency corresponding to the rate at which relay MR isoperated. Secondary winding 55 of transformer AT is connected to theinput terminals of decoding unit DU to whose output side two controlrelays A and L are connected.

The decoding unit DU may be any one of several well-known forms, and itis sufficient for the present application to point outl that relay A isenergized and picked up when the electromctive force applied to decodingunit DU is of a frequency produced by operation of relay MR at the ratecorresponding to the 180 code rate for the track circuit current, andrelay L is effectively energized and picked up and relay A is releasedwhen the electromotive force applied to decoding unit DU is of thefrequency produced by operation of relay MR at the rate corresponding tothe 75 code rate for the track circuit current. Relays A and L are usedto govern the operating circuit of signal CS. These operating circuitswould be of standard practice and it is sufficient to point out thatwhen relay A is picked up closing front contact 56, an operating circuitis formed for a lamp 5l and that lamp is illuminated to cause signal CSto display a clear signal indication. When relay A is released closingback contact e8 and relay L is picked up closing front contact 58, anoperating circuit is formed for a lamp 66 and that lamp is illuminatedcausing signal CS to display an approach signal indication, and whenrelays A and L are released closing back contacts 53 and Si,respectively, an operating circuit is formed for a lamp 62, and thatlamp is illuminated to cause signal CS to display a slow speed signalindication.

In describing the operation of the apparatus of Fig. l, I shall assumethe train TV on which the apparatus is mounted occupies section D--E. Itis to be recalled that normally the electron tube VTI is provided with apredetermined negative grid bias voltage through the battery I, andwhich voltage is such that Zero current flows in the plate circuit ofthe tube. The bias voltage applied to tubes VT? and VT3 is such in eachcase that a predetermined value of current oWs in the respective platecircuit. When the normal value of plate circuit current flows for tubeVT3 no energy is transferred at transformer T5 and master code followingrelay MR is active so that relays A and L are released and lamp 52 isilluminated to display a slow speed cab signal. shall next assume thatrelay HD is picked up and alternating current coded at the code rate isapplied to the track rails of section D-E. During each on period of thecoded rail current electromotive forces are induced in inductors 9 andl0 which electromotive forces are of substantially the same magnitudesince the value of current flowing in each rail is the same andfurthermore, these electromotive forces are in phase with each other.This condition is illustrated in Fig. 2 where the solid line EMIrepresents the electromotive force picked up by inductor 9 and appliedto the first receiving channel cf the train carried apparatus and thedash line EM2 represents the electromotive force picked up by inductorIll and applied to the second receiving channel. During the positivehalf cycle of the electromotive force applied to the rst receivingchannel, the grid i5 of tube VTI is driven in the posiive direction withthe result that the potential of the grid I5 with respect to cathode I'Iis less negative. The electromotive force applied to the second channelis amplified at Lube VTZ and the resultant electromctive force inducedin secondary Winding 36 of transformer T3 is applied to grid iii of tubeVTI and during a positive half cycle of the electromotive force grid I9is driven positive in potential with respect to cathode I'I. Since thesetwo electrometive forces are in phase with each other grids l5 and I9are simultaneously driven positive and current flows in the platecircuit of tube VTI. During the negative half cycle of each of theelectromotive forces, grids I5 and I9 are both more negative and noplate current fiows. The current flowing in the plate circuit of tubeVTI under these conditions is illustrated in Fig, 3 which shows thatduring the positive half cycle of the electromotive forces plate currentflows and during the negative half cycle of the electromotive forces nocurrent ows. This results in a series of half cycle pulses of currentwhich induce an electromotive force in secondary winding 42 of couplingtransformer T4. The circuit made up of condenser 43 and secondarywinding 42 smooths out the electromotive force induced in secondarywinding i2 to form a reasonably smooth sine wave voltage. Theelectromotive force transferred by transformer T is amplified by tubeVTS in the usual manner to cause corresponding variations of the platecircuit current of that tube with the result that there is an increasein the average value of the plate circuit current at the start of eachon period of the ceded current and a corresponding decrease in theaverage value of the plate circuit current at the start of each offperiod of the coded current. Such variations in the plate current 1 ortube VTS induce electromotive forces in secondary winding 50 oftransformer T5 to cause operation of relay MR in the well-known manner.Since the track circuit current is of the 180 code rate, relay MR isoperated at a corresponding code rate so that relay A is picked up andlamp 5'# is illuminated to display a clear signal indication.

In the case relay HD is released and the rail current is coded at the'75 code rate, the operation of the apparatus is the same except for therate at which code following relay MR is operated and with relay MRoperated at the rate corresponding with the 75 code rate of the trackcircuit current, relay L is picked up and relay A is released causinglamp 6i) to be illuminated to display an approach signal indication.

As pointed out hereinbefore when relay MR is inactive as in the casewhen no coded current is supplied to the track circuit then relays A andL are both released and signal lamp 62 is illuminated to display a slowspeed signal indication.

Figs. 4 and 5 illustrate the action when the electromotive forcesinduced in inductors 9 and I are shifted by as much as 90 degrees out ofphase. Since plate current can flow for tube VTI only when both grids I5and I9 are driven positive by a predetermined amount, then when theelectromotive forces are shifted 90 degrees out of phase, both grids I5and I9 are driven positive for only a quarter cycle and even then theirproducts are quite small. The resultant plate circuit is illustrated inFig. 5. These pulses of plate circuit current are effective to induceelectromotive forces in secondary winding 42 of coupling transformer Tdbut `such electromotive forces even when amplified by tube VTS are notsufficient to cause operation of code following relay MR. It

is to be observed that if the electromotive forces induced in inductors9 and I0 are out of phase more than 90 degrees practically no platecurrent would flow for tube VTI and no energy would be applied to thecode following relay MR.

In the event sc-called magnetized spots exist in either rail I a. andlb-, that is, there are spots which in effect appear to be permanentlymagnetized, an electromotive force may be induced in inductor 9 whensuch a magnetized spot exists in rail la and may be induced in inductorI0 when such a spot occurs in rail Ib when the corresponding inductorspass over the magnetized spots in the respective rail. In the event suchan electromotive force is induced in inductor 9 and applied to grid I5of tube V'II and this stray electromotive force is such as to drive gridI5 in the positive direction no plate current fiows in the tube due tothe high negative bias voltage effected by battery I6 because grid I9 isnot at the same time excited. If the stray electromotive force isinduced in inductor ID and applied to grid I9 to drive that grid in thepositive direction no plate current fiows for tube VTI due to the biasof battery I6 because grid I5 'is not at the same time excited. For'suchmagnetized spots in the track rails to cause a fiow of plate current,such spots must occur opposite each other and of a lpolarity that thestray electromotive forces induced in inductors 9 and Ii) drive bothgrids I5 and I 9 in the positive direction simultaneously. Thesemagnetized rail spots are random and the possibility of the last citedcondition occurring is very remote.

Again stray electromotive forces induced in inductors 9 and It] from anadjacent power line would be 180 degrees out of phase and for thereasons pointed out hereinbefore would produce no flow of plate currentin tube VTI and hence no operation of relay MR.

If one track rail is broken current might flow in the other rail atabout the usual magnitude due to the ballast leakage, but the current inthe broken rail would be considerably less, and hence while one grid I5or I9 might be excited in the usual manner, the excitation of the othergrid would be absent or very small and sufficient plate current to causeoperation of relay MR would not be effected.

While indirect heater type tubes are shown in Fig. 1, it is clear thatother types of tubes may be used. Also tubes VTI and VT2 maybe combinedin one tube structure such as a petrodetriode tube. If furtheramplification is needed a stage of amplification could be included inthe receiving channels in advance of tubes VTI and VT2. Furthermore thefinal state of amplification including tube VT3 may not be required.

It is clear that I have provided railway traffic controlling apparatusincorporating a novel and improved electron tube amplifier wherewith theelectromotive force picked up from one rail of a track circuit isapplied through one receiving channel to a first control grid of theamplifier tube, and the electromotive force picked up from the otherrail of the track circuit is applied through another receiving channelto a second control grid and plate current fiows for the tube only Whenthese two electromotive forces are simultaneously applied to therespective grids and the electromotive forces are substantially in phasewith each other.

Although I have herein shown and described Vonly one form of railwaytraffic controlling apparatus embodying my invention, it is understoodthat various changes and modifications may be made therein within thescope of the appended claims without departing from the spirit and scopeof my invention.

Having thus described my invention, what I claim is:

1. In combination, a track section, means to supply coded alternatingcurrent from a preselected source across the rails of the section tocause such current to fiow in the rails in series, a train to travelsaid section; a train carried electron tube having a plate, a cathodeand a first and a second grid; a first circuit means on the traincoupled to one I,of the track rails only and connected across the firstgrid and cathode of said tube to create an alternating electromotiveforce between the first grid and cathode each on period of such codedcurrent, a second circuit means on the train coupled to the other trackrail only and including a transformer whose secondary winding isconnected across the second grid and cathode of said tube to create analternating electromotive force between the second grid and cathode eachon period of such coded current, a plate circuit including a currentsource connected across the plate and cathode of said tube, meansincluding a source of direct voltage connected to said first grid andcathode to create a predetermined negative grid bias voltage which isineffective to prevent a flow of current in said plate circuit only whensaid electromotive forces are created between the respective grids andcathodes simultaneously and in phase with each other, said first andsecond circuit means disposed to create said alternating electromotiveforces in phase to cause plate current to flow in response to railcurrent supplied by said preselected source only, and a train carriedtrain control means coupled to said plate circuit effectively governedby the current thus caused to flow in the plate circuit.

2. In combination, a track section, means to supply coded alternatingcurrent from a preselected source across the rails of the section tocause such current to fiow in the rails in series, a train to travel thesection; a train carried electron tube having a plate, va cathode, acontrol grid and another grid; a first circuit means on the trainincluding a winding coupled to one of the track rails only and connectedacross the `control grid and cathode of the tube to impress on thecontrol grid an alternating electromotive force in response to saidcoded current owing in said one rail, a second circuit means on thetrain including a winding coupled to the other one of the track railsonly and another electron tube amplifier and a transformer having awinding connected across the other grid and cathode of the firstmentioned tube to impress on said other grid an amplified alternatingelectromotive force in response to said coded current flowing in saidother rail, a plate circuit including a Winding and a current sourceconnected across said plate and cathode of said first mentioned tube,means including a source of direct voltage connected across said controlgrid and cathode of the rst mentioned tube to provide a predeterminednegtaive grid bias voltage for that tube to permit current to iiow insaid plate circuit only when said electromotive forces are impressed onthe respective grids of said first mentioned tube simultaneously and inphase with each other, said first and second circuit means disposed toimpress said alternating electromotive forces in phase on the respectivegrids to create a plate current only in response to said coded currentsupplied by said preselected source, and a code following relay coupledto said plate circuit winding to operate the relay by the current thuscaused to flow in said plate circuit.

3. In railway traflic controlling apparatus for use with a track sectionwhose track rails are supplied with coded alternating current whichflows in the rails in series, the combination comprising; an electrontube having a plate, a cathode and a rst and a second grid; a iirstreceiving channel electrically coupled to one rail only of the sectionand connected across said first grid and cathode of said tube to impressupon said first grid an alternating electromotive force in response toeach on period of said coded cur rent flowing in said one rail, a secondreceiving channel electrically coupled to the other rail only of thesection and connected across said second grid and cathode of said tubeto impress upon said second grid an alternating electromotive force inresponse to each on period of said coded current flowing in said otherrail, a plate circuit including a winding and a current source connectedto said plate and cathode of the tube, means including a source ofdirect voltage connected across said first grid and cathode of the tubeto provide a preselected negative grid bias voltage for the tube tocause no current to normally flow in said plate circuit and to permitplate current to flow only when said electromotive forces are applied tothe respectlve grids simultaneously and in phase with each other, saidrst and secondreceiving channels poled to impress said alternatingelectromotive forces on the respective grids in phase to provide a platecurrent only during an on code period of the current supplied by saidpreselected source, and a code following relay coupledr to said platecircuit winding eifectively operated by the plate current thus caused toiiow in said plate circuit.

4. In railway traciiic controlling apparatus for use with a tracksection whose rails are supplied with coded alternating current, thecombination comprising, two inductors mounted one for inductive relationto one rail of the track section and the other for inductive relation tothe other rail; an electron tube having a plate,

a cathode and a first and a second grid; means to couple a first one ofsaidV inductors to the rst grid and cathode of said tube to apply acrosssaid first grid and cathode the alternating electromotive force inducedin said one inductor each on period of such coded current, meansincluding a transformer having a winding connected directly across saidsecond grid and cathode to couple the second one of said inductors tothe second grid and cathode of said tube to apply across said secondgrid and cathode the alternating electromotive force induced in saidsecond inductor each on period of the coded current, a plate circuit forsaid tube and including a winding and a current source, means connectedto at least one of said grids and the cathode tof provide apredetermined negtaive bias voltage: for the tube that causes no currentto normally iiow in said plate circuit and permits plate cur'- rent toflow only when said electromotive forces are applied to the respectivegrids in phase to drive the grids in the positive directionsimultaneously, said inductors poled to apply said electromotive forcesto the respective grids in phase, and a code following relay coupled tosaidV plate circuit winding to operate the relay in respense to theplate current thus caused to flow.

5. In railway traiiic controlling apparatus for use with a track sectionwhose rails are supplied with coded current from a preselected source ofalternating current, the combination comprising, two inductors mountedone for inductive relation to one rail of thel track section and theother for inductive relation to the other rail; an electron tube havinga plate, a cathode and a first and a second grid; means to couple afirst one oi said inductors to the rst grid and cathode of said tube toapply across said first grid and cathode the alternating electromotiveforce induced in said one inductor each on period of such coded current,means including a transformer having a winding connected directly acrosssaid second grid and cathode to couple the second one of said inductorsto the second grid and cathode of said tube to apply across said secondgrid and cathode the alternating electromotive force induced in saidsecond inductor each on period of the coded current, a plate circuit forsaid tube and including a winding and a current source, means connectedto a selected one of said grids and the cathode to provide apredetermined negative bias voltage for the tube to normally cause zeroplate current and to permit plate current to flow only when saidelectromotive forces are applied to the respective grids simultaneouslyand in phase with each other, said inductors poled to apply therespective electromotive forces to the respective grids in phase witheach other tov cause plate current to flow due to current supplied bysaid preselected source, and a code following relay coupled to saidplate circuit winding to operate the relay in response to the platecurrent thus caused to flow.

6. In railway trame controlling apparatus for use with a track sectionwhose track rails are supplied with coded current from a preselectedsource of alternating current, the combination comprising, two inductorsmounted one for inductive relation to one of the track rails of thesection and the other for inductive relation to the other track rail; afirst electron tube having a plate, a cathode, a control grid andascreen grid; a first receiving channel to couple a selected one of saidinductors to the controlV grid and cathode of said tube to apply acrossthe control grid and cathode the alternating electromotive force inducedin said first inductor each on period of such coded current, a seconde1ec tron tube, a transformer provided with a primary Winding includedin the plate circuit of said second tube and a secondary Windingconnected directly across said screen grid and cathode of said firsttube, a second receiving channel including said second electron tube andsaid transformer to couple the other inductor to the screen grid andcathode of said rst tube to apply across the screen grid and cathode ofthe first tube the alternating electromotive force induced in said otherinductor by each on period of the coded current when amplified by saidsecond tube, a plate circuit `for said rst tube including a Winding anda current source, and a code following relay coupled to saidplatecircuit winding to operate said relay in response to the variationsin the plate current of said rst tube effected only when theelectromotive forces applied to the control grid and screen grid of thefirst tube are in phase with each other.

'7. In combination, a track section, means to supply alternating currentfrom a preselected source across the rails at the exit end of thesection to cause such current to flow in the rails in series, a train totravel the section; a train carried electron tube having a plate, acathode and a first and a second grid; a rst receiving channel on thetrain including a winding coupled to one of the rails only of thesection and connected across the rst grid and cathode of said tube toimpress between the rst grid and cathode an alternating electromotiveforce in response to said alternating current owing in said one rail, asecond receiving channel on the train including a Winding coupled to theother rail only of the section and a transformer provided with asecondary Winding connected directly across the second grid and cathodeof said tube and said second channel eiective to impress between thesecond grid and cathode an alternating electromotive force in responseto said alternating current flowing in said other rail, a plate circuitincluding a current source connected across the plate and cathode ofsaid tube, means including a source of direct voltage connected acrossthe rst grid and cathode of the tube to create a predetermined negativegrid bias voltage for the tube, said receiving channels poled to impresssaid electromotive forces in phase on the respective grids to overcomesaid negative bia-s voltage each positive half cycle of saidelectromotive forces to cause plate current to iiow only in response tocurrent supplied by said preselected source, and a train carried traincontrol means governed by said plate circuit and effectively energizedin response to the current thus caused to flow in the plate circuit.

W'ILLARD P. PLACE.

